Control system and method for supplying pressure means to at least two hydraulic consumers

ABSTRACT

Disclosed are a control arrangement and a method for the pressure medium supply of at least two hydraulic consumers that are supplied with pressure medium through the intermediary of a variable displacement pump. In the pressure medium flow path between the consumers and the variable displacement pump a respective meter-in orifice is provided. An adjustment of the variable displacement pump and of the meter-in orifices takes place electronically through the intermediary of a control means in dependence on the target values input by an operator. In accordance with the invention, the meter-in orifice associated with the consumer having the highest load pressure is controlled to open completely, so that the pressure loss across this meter-in orifice is minimum.

The invention relates to a control arrangement for the pressure mediumsupply of at least two hydraulic consumers and a method for controllingsuch consumers.

In order to actuate several consumers, hydraulic systems are employed inwhich the consumers are supplied with pressure medium through theintermediary of a pump having a variable capacity (variable displacementpump). Between the variable displacement pump and each consumer ameter-in orifice and a pressure compensator are frequently provided,wherein the latter may be arranged upstream or downstream from themeter-in orifice. Here one differentiates between LS (load-sensing)systems operating according-to the flow regulator principle and systemsoperating according to the flow divider principle, where the pressurecompensator is always arranged downstream from the meter-in orifice.These flow divider systems are also referred to as systems withload-independent flow distribution load independent flow distributionLUDV), which constitute a subgroup of the LS systems. In the LS systems,the variable displacement pump is adjusted in dependence on the highestload pressure of the actuated hydraulic consumers, such that the supplypressure is higher than the highest load pressure by a specific pressuredifference.

In LUDV systems, the pressure compensators arranged downstream aresubjected to the pressure downstream from the respective meter-inorifice in the opening direction, and to a control pressure whichusually corresponds to the highest load pressure of all the actuatedconsumers in the closing direction. If, upon concurrent actuation ofseveral hydraulic consumers, the meter-in orifices are opened to such anextent that the quantity of pressure medium supplied from the hydraulicpump adjusted to the limit is smaller than the total demanded quantityof pressure medium, the quantities of pressure medium flowing to thesingle hydraulic consumers are reduced proportionally, independently ofthe respective load pressure of the hydraulic consumers(load-independent flow distribution).

In systems operating in accordance with the flow regulator principle,the pressure compensator arranged upstream or downstream from themeter-in orifice is subjected to the pressure upstream from the meter-inorifice in the closing direction, and to the individual load pressure ofthe respective hydraulic consumer in the opening direction, whereby aload-independent flow distribution is not obtained. If several hydraulicconsumers are actuated simultaneously while not being supplied with asufficient quantity of pressure medium delivered from the variabledisplacement pump, only the quantity of pressure medium flowing to thehydraulic consumer having the highest load pressure is reduced.

Such a control arrangement is disclosed, e.g., in EP 0 972 138 B1,wherein the pressure compensators are arranged upstream from themeter-in orifices. In DE 100 27 382 A1 a LS control arrangement isrepresented wherein the pressure compensators are arranged downstreamfrom the meter-in orifices.

In all of the above described LS/LUDV systems, the variable displacementpump is driven in dependence on the highest load pressure that is tappedvia a LS line, so that a pressure manifests in the pump line which ishigher than the highest load pressure by a pressure differenceequivalent to the force of a control spring of a pump control valve. Inthe periodical O+P “oil hydraulics and pneumatics” 38 (1994), No. 8, pp.473 et seq., a so-called electro-hydraulic LS system is described inwhich the regulation of the pump setting is performed electronically.Among others, the pressures acting on the consumers, the pump pressure,the drive speed, and the drive torque of the variable displacement pumpare detected by sensors, and actuation signals are output in dependence,e.g., on target values predetermined through the intermediary of ajoystick to the pump regulating valve and the proportional valvesarranged upstream from the consumers. In this known electro-hydraulicsystem, the function of the individual pressure compensators associatedwith the meter-in orifices is realized electronically.

In this solution, too, the pump pressure is adjusted such that isexceeds the highest load pressure by a predetermined pressuredifference, so that corresponding system losses may occur in this typeof actuation.

In EP 0 275 969 B1 an electro-hydraulic LS control arrangement is shownwhere the individual pressure compensators are arranged upstream fromthe meter-in orifices. In this known method, the target values set forthe meter-in orifices through the intermediary of actuators, e.g.,joysticks, are detected and a total flow rate is determined from them.Driving the variable displacement pump then takes place such that aslight insufficient supply manifests, so that the meter-in orifice ofthe consumer having the highest load pressure is opened, and thus theabove mentioned pressure difference between the pump pressure and thehighest load pressure is reduced. Due to this insufficient supply,however, the actuation velocity of the consumers is reduced.

From DE 35 46 336 C2 and DE 36 44 736 A1 electro-hydraulic LS systemsare known in which the total flow rate is determined either from thedeflections of the directional control valves constituting the meter-inorifices or from the settings of the target value entry means(joystick), and this cumulative flow rate is compared with a maximumcapacity of the pump. In a case in which more capacity is requested, thestrokes of all of the actuated directional control valves areelectrically reduced to such a degree that the respective flows arereduced proportionally, and thus the adjusted trajectory of the actuatedconsumers is preserved at a reduced actuation velocity.

In these solutions, as well, a pressure loss corresponding to thedifference between the pump pressure and the individual load pressuremanifests at the meter-in orifice of consumer subjected to the highestload.

In contrast, the invention is based on the object of further developinga control arrangement and a method for the pressure medium supply of atleast two hydraulic consumers in such a way that an actuation of severalconsumers with a predetermined velocity at reduced energy losses isenabled.

This object is achieved in terms of the control arrangement through thefeatures of claim 1, and in terms of the method through the features ofclaim 6.

In accordance with the invention, the individual load pressures of theconsumers are detected through suitable sensors, and from these signalsthe consumer having the highest load pressure is determined. Themeter-in orifice associated with the consumer having the highest loadpressure is controlled open completely by the setting resulting from thepreset target value, so that the pressure loss across the meter-inorifice associated with the consumer having the highest load is minimum.In the event of a sufficiently accurate harmonization between thepressure medium flow rates through the meter-in orifices predeterminedby the target values and the capacity, only a minimum pressuredifference is caused at the meter-in orifice of the consumer having thehighest load. In a case in which an individual pressure compensator isassociated with this meter-in orifice, the latter is also openedcompletely, for even a slight excess quantity of the pressure mediumflow rate delivered by the pump is not suited to generate, at thecompletely opened meter-in orifice, a pressure drop capable of adjustingthe pressure compensator in the closing direction against the force of acontrol spring associated with the latter.

The control arrangement of the invention, or the method of theinvention, may be employed in control arrangements where the individualpressure compensators are arranged upstream or downstream from themeter-in orifices.

In a case in which the control arrangement in accordance with theinvention is executed with another sensor for detection of the systempressure, i.e., the pressure upstream from the meter-in orifices, thepressure difference across the respective meter-in orifices may bedetermined with the aid of the signals detected by the pressure sensors.The meter-in orifices are then adjusted by means of the electronicequipment of the control arrangement such that the desired pressuremedium flow rate flows to the consumers. I.e., in such a variant thefunction of the individual pressure compensators is realizedelectronically, in which case, however, in contrast with the literature(O+P) mentioned at the outset, the meter-in orifice of the consumerhaving the highest load pressure is always opened completely, so thatthe energy losses are reduced in comparison with the known solution.

As an alternative for the above described solution where the function ofthe individual pressure compensators is realized by software, thecontrol arrangement may be executed with individual pressurecompensators arranged upstream or downstream from the meter-in orifices,that are each subjected to the pressure upstream from the meter-inorifice in the closing direction, and to the pressure downstream fromthe meter-in orifice in the opening direction.

In the variant where the pressure compensators are arranged downstreamfrom the meter-in orifices, there results a structure similar to that ofLUDV directional control valves. This makes it possible to provideidentical or at least similar housings as semi-finished products for thecontrol arrangement in accordance with the invention and LUDV controlarrangements, so that the manufacturing costs may be reduced.

In the case of a pulling load, it is possible to detect this by means ofthe sensors used in accordance with the invention and to throttle downthe variable displacement pump, and the pressure medium may bereplenished to the low-pressure side of the consumers viaanti-cavitation valves.

By the method in accordance with the invention, in the case of ainsufficient supply the flow passages of the meter-in orificesassociated with the consumers having lower loads may be reducedproportionally. This reduction preferably takes place with the ratio ofthe maximum pump capacity to the desired target quantity.

In a practical example of the method of the invention, the loadpressures of simultaneously actuated consumers are compared, and in acase in which these load pressures differ by less than the regulating Δpof the pressure compensators, the meter-in orifice of the consumerhaving a lower load is opened further than predetermined by the targetvalue, so that this pressure difference is compensated.

Further advantageous developments of the invention are subject matter offurther subclaims.

In the following, preferred practical examples of the invention shall beexplained in more detail by referring to schematic drawings, where:

FIG. 1 shows a control arrangement in accordance with the invention,with individual pressure compensators arranged downstream from themeter-in orifices;

FIG. 2 shows a variant of the control arrangement of FIG. 1, with anupstream individual pressure compensator;

FIG. 3 shows a control arrangement where the function of the individualpressure compensators is realized electronically, and

FIG. 4 shows a control arrangement with individual pressure compensatorsarranged downstream from the meter-in orifices.

The control arrangement 1 represented in FIG. 1 operates in accordancewith the flow regulator principle where several flow regulators arearranged in parallel. The represented control arrangement 1 has avariable displacement pump 2 whereby two or more consumers 4, 6 may besupplied with pressure medium. Their actuation takes place, e.g., withthe aid of a control device, for instance a joystick 8, whereby controlsignals are output to electronic control means 10. These signalsconstitute a command to displace the consumers at a particular velocityand along a particular movement path.

The outlet from the variable displacement pump 2 is connected to a pumpline 12 branching into two supply lines 14, 16. In each supply line 14,16 a respective meter-in orifice 18 or 20 is arranged which mayelectronically be adjusted proportionally and which may be adjustedthrough the intermediary of a proportional magnet 22 driven by thecontrol means 10.

The meter-in orifices 18, 20 formed, e.g., by proportional valves areeach followed by a pressure compensator 24 or 26, respectively, which issubjected in the opening direction to the force of a control spring andto the pressure downstream from the meter-in orifices 18, 20, and whichis subjected in the closing direction to the pump or system pressuretapped from the pump line 12 via a branched control line 28.

The outlets of the pressure compensators 24, 26 are connected via arespective delivery line 30 and 32 with the consumers 4, 6. In thepresent case, these consumers 4, 6 are hydraulic cylinders, the cylinderchambers of which are coupled to the respective delivery line 30 and 32.In the hydraulic circuit diagram in accordance with FIG. 1, for the sakeof simplicity the return and drain lines connecting the cylinderchambers with the tank T have been omitted, whose cross-sections of floware equally controlled to open or close through the intermediary of theproportional valve forming the meter-in orifice 18, 20.

In accordance with the invention the load pressures of the consumers 4,6 are detected and the settings of the meter-in orifices 18, 20 arealtered in dependence on these load pressures. In the representedpractical example, these load pressures are detected by pressure sensors34, 36 which are arranged in the delivery lines 30, 32 and the signalsof which are processed by the control means 10. In accordance with therepresentation in FIG. 1, the pressure sensors 34, 36 as well as thejoystick 8 are connected via signal lines with the control means 10,whereby control signals are then output via signal lines to theelectrically actuated pump regulating valve as well as the twoproportionally adjustable meter-in orifices 18, 20 in accordance withthe predetermined target values and the detected load pressures.

Instead of a variable displacement pump having a variable swivel angle,it is, for instance, also possible to use a fixed displacement pumphaving a variable-speed drive mechanism.

The variable displacement pump 2 is preferably executed with a pressuresensor for detecting the pump pressure, a speed sensor for detecting thepump speed, and a swivel angle sensor for detecting the swivel angle ofthe pump. Inside the control means the characteristics of the variabledisplacement pump 2 and of the two proportionally adjustable meter-inorifices 18, 20 are moreover stored, so that with the aid of all, orsome of, the above mentioned sensors and-of the characteristics, anextremely accurate flow rate control by means of the variabledisplacement pump 2 is possible. The operation of the controlarrangement in accordance with the invention is as follows.

In order to actuate the two consumers 4, 6, control signals aregenerated by the operator with the aid of one or more joysticks 8 andoutput to the control means 10. For correspondingly actuating theconsumers 4, 6, the variable displacement pump 2 has to provide aparticular pressure medium flow rate corresponding to the sum of thetarget flow rates adjusted by means of the joystick 8. In other words,the variable displacement pump 2 must be adjusted, in dependence on theadjustment of the joystick 8, to a swivel angle at which this cumulativeflow rate is delivered. The corresponding adjustment of the variabledisplacement pump 2 may in a simple manner be achieved in dependence onthe target value by detecting the current pump pressure, the currentpump speed, and the adjusted swivel angle with the aid of the pumpcharacteristic.

In accordance with the invention, the pump controller thus does notreceive a pressure signal that corresponds, as a rule, to the highestload pressure, but actuation of the variable displacement pump 2 isperformed solely in dependence on the target values. This does away withthe necessity of tapping the load pressures via complex shuttle valvearrangements at the consumers and conducting them via comparatively longlines to the variable displacement pump 2.

Thanks to the target value adjustment with the aid of the joystick 8 itis possible to compensate flow rate errors occurring as a result ofvolumetric losses of the variable displacement pump 2, for the operatorwill immediately perform a readjustment with the aid of the joystick 8if the consumers 4, 6 are not actuated at the desired velocity. Thehighest load pressure then accordingly manifests at the consumersubjected to the highest load, and the pressure difference from theconsumers subjected to lower loads is throttled away by a flow controlat the individual pressure compensators 24, 26.

In accordance with the invention, the one consumer at which the highestload pressure is present is determined by way of the pressure sensors34, 36. To this end, the signals detected by the pressure sensors 34, 36are compared to each other in the control means 10, and a control signalis output to the one meter-in orifice 18, 20 associated to the consumer4, 6 having the highest load pressure, whereby this meter-in orifice 18,20 is opened fully. Then only a minimum pressure difference is caused atthis meter-in orifice 18, 20, so that the system losses are reduced incomparison with the control options described at the outset. Theassociated pressure compensator 24 or 26 of the respective consumer 4 or6 having the highest load pressure is then also opened completely, forthe pressure difference across the associated meter-in orifice 18 or 22is not sufficient for adjusting the pressure compensator in the closingdirection against the force of the control spring.

In the practical example represented in FIG. 1, the flow regulationarrangement is executed with the pressure compensators 24, 26 arrangeddownstream from the meter-in orifices 18, 20. As the pressurecompensators must always be arranged downstream from the meter-inorifices in the LUDV systems described at the outset, identical housingsor housings only slightly modified may be used for the systemrepresented in FIG. 1 and for LUDV systems.

As is indicated in FIG. 2, the control arrangement in accordance withthe invention may also be realized in control arrangements where theindividual pressure compensators 24, 26 are arranged upstream from themeter-in orifices 18 and 20. These pressure compensators are alsosubjected in the opening direction to the pressure downstream from themeter-in orifices 18, 20, and in the closing direction to the pressureupstream from the meter-in orifices 18, 20, i.e., to the pump pressuredelivered by the variable displacement pump 2. The remaining structureand the function of the control arrangement represented in FIG. 2correspond to the practical example in accordance with FIG. 1, so thatadditional explanations are not necessary.

In FIG. 3 a variant is represented where no individual pressurecompensators are associated to the meter-in orifices 18, 20. In thispractical example, the function of the individual pressure compensatorsis practically taken over by the electronic equipment. To this end, thepressure in the pump line 12, i.e., the pressure upstream from themeter-in orifices 18, 20, must be detected by an additional pressuresensor 38. It is then possible to calculate the pressure drop across themeter-in orifices 18, 20 from this pressure and from the pressuresdownstream from the meter-in orifices 18, 20 that are detected by thepressure sensors 34, 36. Having knowledge of these pressure lossesacross the meter-in orifices 18, 20, the cross-section of flow of therespective meter-in orifices 18, 20 may then be adjusted through thecontrol means 10 with the aid of the stored characteristic lines, suchthat the desired flow rate flows to the consumers 4, 6. The adjustmentof the variable displacement pump 2 is performed in the above describedmanner in-dependence on the target values set through the joystick 8.

The above described systems differ from the previously known LS systemsin that the variable displacement pump is adjusted to the desiredcumulative flow, and the single pressure medium flows to the consumersare divided up by suitable control of the valve orifices, wherein themeter-in orifice associated with the consumer having the highest loadpressure is controlled to open completely.

Such a control arrangement makes it possible, e.g., in the case ofinsufficient supply, i.e., in a case in which the target quantity isgreater than the maximum pump quantity, to proportionally reduce theflows passing through the meter-in orifices of the consumers havinglower load pressures. I.e., by the control arrangement in accordancewith the invention it is practically possible to achieve a LUDV behaviorin that the opening cross-sections of the meter-in orifices 18, 20having lower load pressures are reduced. This reduction may, e.g., takeplace at the ratio of the maximum pump capacity to the target quantity.This shall be explained by way of an example where the controlarrangement of the invention is realized for actuating three consumers.It shall furthermore be assumed that the target flows at the threeconsumers set through joysticks 8 are 40, 60 and 20 liters/minute, i.e.,the target cumulative flow rate is 120 liters/minute, where the consumerhaving the highest load pressure is to be supplied with 20liters/minute. The maximum capacity of the pump is, e.g., 100liters/minute—which is an insufficient supply. This insufficient supplyis compensated, in accordance with the invention, in that the targetvalues for the two consumers having lower loads (40, 60 liters/minute)is reduced through the intermediary of the control means 10 at the ratioof the maximum capacity of the pump to the cumulative flow rates, i.e.,at a ratio of 100/120. In other words, the consumer named first issupplied with 33.33 liters/minute, the consumer named second with 50liters/minute (per time unit). The meter-in orifice of the consumerhaving the highest load pressure is controlled fully open in accordancewith the invention—the manifesting flow rate across this meter-inorifice is 16.66 liters/minute, so that the maximum capacity of thepump, being 100 1/min., is divided at an identical ratio and thus aload-independent flow distribution (LUDV) is realized in practice.

In a case in which a pulling load is acting (such as in downhilltravel), this may be detected through the pressure sensors 34, 36, andthe pump may be regulated down accordingly. Replenishing on thelow-pressure side of the consumers 4, 6 then takes place viaanti-cavitation valves from the high-pressure side. In other words, incomparison with presently usual control arrangements, the losses in thecase of a pulling load may be reduced further.

Particularly the practical examples explained by reference to FIGS. 1and 2 are characterized by a low susceptibility to vibration.

The target values may, instead of the electric joystick 8, even in thecase of proportional valves provided with spool stroke measurement, bedetermined from the actual spool stroke value of the meter-in orifices18, 20.

The system in accordance with the invention is, of course, alsoeffective when only a single consumer is actuated—in this case, themeter-in orifice of this consumer is controlled to open completely, andthe pressure medium flow rate is controlled through the variabledisplacement pump 2.

FIG. 4 shows a control arrangement where the individual load pressuresof the consumers 4, 6 are not detected by means of pressure sensors orthe like. This is in turn a flow regulation system in which the twoindividual pressure compensators 24, 26 are arranged downstream from thetwo proportionally adjustable meter-in orifices 18, 20. In other words,apart from the fact that the two sensors 34, 36 are not provided, thecontrol arrangement represented in FIG. 4 corresponds to the one ofFIG. 1. In the control arrangement in accordance with FIG. 4, as well,the variable displacement pump 2 is adjusted as a function of the targetvalues set through the intermediary of the joystick 8 such that itdelivers the desired cumulative pressure medium flow. Dividing of thiscumulative pressure medium flow then is effected by means of the flowregulators (meter-in orifices 18, 20; pressure compensators 24, 26),with the meter-in orifices 18, 20 again being adjusted as a function ofthe target values set at the joystick 8. By means of the individualpressure compensators 24, 26 the load pressure present at the outlet ofthe meter-in orifices 18, 20, which about corresponds to the highesteffective load pressure of the consumers, is throttled to the individualload pressures. As a difference from the above described practicalexample, however, the meter-in orifice associated with the consumerhaving the higher load pressure remains at the opening cross-section setas a function of the predetermined target value and is not controlledopen completely.

Disclosed are a control arrangement and a method for the pressure mediumsupply of at least two hydraulic consumers that are supplied withpressure medium through the intermediary of a variable displacementpump. In the pressure medium flow path between the consumers and thevariable displacement pump a respective meter-in orifice is provided. Anadjustment of the variable displacement pump and of the meter-inorifices takes place electronically through the intermediary of acontrol means in dependence on the target values input by an operator.In accordance with the invention, the meter-in orifice associated withthe consumer having the highest load pressure is controlled to opencompletely, so that the pressure loss across this meter-in orifice isminimum.

LIST OF REFERENCE SYMBOLS

-   1 control arrangement-   2 variable displacement pump-   4 consumer-   6 consumer-   8 joystick-   10 control means-   12 pump line-   14 supply line-   16 supply line-   18 meter-in orifice-   20 meter-in orifice-   22 proportional magnet-   24 pressure compensator-   26 pressure compensator-   28 control line-   30 delivery line-   32 delivery line-   34 pressure sensor (load pressure)-   36 pressure sensor (load pressure)-   38 pressure sensor (pump pressure)

1. A control arrangement for the pressure medium supply of at least twohydraulic consumers, comprising a variable displacement pump arrangementwhich has a variable capacity, and comprising at least two adjustablemeter-in orifices each associated with a respective one of the consumersand respectively adjustable in dependence on a target value set at atarget value entry means through the intermediary of a control means,and comprising a means outputting a control signal to the variabledisplacement pump in dependence on the set target values, characterizedby respective sensors provided in the pressure medium flow pathsdownstream from the meter-in orifices for detecting the individual loadpressures, by a means for detecting the consumer having the highest loadpressure based on the signals detected by the sensors and forcontrolling open the meter-in orifice associated with the consumerhaving the highest load pressure, wherein upstream or downstream fromeach meter-in orifice a pressure compensator is arranged which issubjected in the closing direction to the pressure upstream from themeter-in orifice, and in the opening direction to the pressuredownstream from the associated meter-in orifice.
 2. The controlarrangement in accordance with claim 1, wherein an additional sensor isprovided for detecting the pressure upstream from the meter-in orifices,and wherein the pressure drop across the meter-in orifices is determinedwith the aid of the means from the detected signals, and the actuationof the meter-in orifices is variable in dependence on this pressuredrop, so that a desired pressure medium flow rate flows to theconsumers.
 3. The control arrangement in accordance with claim 1,wherein the target value entry means is at least one joystick.
 4. Amethod for actuating a control arrangement for the pressure mediumsupply of at least two hydraulic consumers, comprising a variabledisplacement pump arrangement which has a variable capacity, andcomprising at least two adjustable meter-in orifices each associatedwith a respective one of the consumers and respectively adjustable independence on a target value set at a target value entry means throughthe intermediary of a control unit, and comprising a means outputting acontrol signal to the variable displacement pump in dependence on theset target values, characterized in that the individual load pressuresof the consumers are detected, and the meter-in orifice associated withthe consumer having the highest load pressure is controlled to opencompletely, wherein upstream or downstream from each meter-in orifice apressure compensator is arranged which is subjected in the closingdirection to the pressure upstream from the meter-in orifice, and in theopening direction to the pressure downstream from the associatedmeter-in orifice.
 5. The method in accordance with claim 4, wherein apressure upstream from the meter-in orifices is detected, and from thisthe pressure drop across the respective meter-in orifices and theindividual load pressures is determined, and the setting of saidmeter-in orifices is varied such that a desired pressure medium flowrate distribution across the meter-in orifices is established.
 6. Themethod in accordance with claim 4, wherein in the case of aninsufficient supply the cross-sections of flow of the meter-in orificesassociated with the consumers having the lower load pressure arereduced, preferably at the ratio of the maximum pump capacity to thetarget cumulative flow rate.
 7. The method in accordance with claim 4,wherein a pulling load is recognized by evaluating the signals detectedby the sensors, and the variable displacement pump is regulated downaccordingly.
 8. The method in accordance with claim 4, wherein in thecase of a concurrent actuation of several consumers, their loadpressures are compared, and in the case of a differential load pressurebeing less than a control Δp of the pressure compensator, the meter-inorifice associated with the consumer having the lower load pressure iscontrolled to open to such a degree that this load pressure differenceis compensated.